1. Field of the Invention
The present application relates to an infection-resistant polyurethane foam, in particular a hydrophilic polyurethane foam, in which the antiseptic polyhexamethylenebiguanide (PHMB) and/or its hydrochloride is present in the PU foam layer in microparticulate and/or homogeneously dissolved form as well as a superabsorbent, a process for its production and its use in wound contact materials.
2. Description of Related Art
There is a general commitment in medicine to use infection-resistant materials to achieve the best possible control of infections on contact of exogenous material with injured tissue or with bodily fluids. Owing to their versatile properties and flexible shaping, polymeric materials of construction which have been rendered infection-resistant are particularly suitable for the fabrication of medical devices or ancillary equipment.
U.S. Pat. No. 4,479,795 A describes medical equipment composed of permeable polymers containing releasable microbicidal substances capable of diffusing to the surface of the polymer, in particular carboxylic acids.
U.S. Pat. No. 5,451,424 A describes a method of preparing a medical article from a homogeneous polymeric melt, in particular polyurethane or polyurethane-siloxane block copolymers, and chlorhexidine.
WO 96/22114 A describes a medical device comprising polyurethane as a polymeric material in which a microbicidal agent, triclosan, is present as a plasticizer at up to 30% by weight in a homogeneous solution. The polyurethane described is produced by blending a polyurethane resin with the triclosan.
GB 2085454 A describes the use of a microbicidal comonomer to make a microbicidal polymer.
A microbicidal polymeric material for producing medical equipment comprising PHMB as a microbicidal agent which is present in the polymeric carrier in microparticulate form is not described in this context.
Large or chronic wounds are particularly prone to become infected. Antiseptic polymeric wound contact materials shall prevent infections in a reliable and skin-compatible manner and thereby provide sustained support for the healing process.
WO 03/066116 A1=US 2003/0149406 A1 describes multilayered polymeric wound dressings composed of polyurethane foam, preferably of HYPOL, in which therapeutically acting substances can be incorporated. At least one of the layers is a hydrogel to cover the wound. The active ingredient or ingredients are dispersed in the polymeric carrier or enclosed in micelles. Release of the therapeutic ingredient from the micelles is limited to the micelles close to the surface.
US 2004/0018227 A1 describes three-layered wound dressing consisting inter alia of a porous polyurethane foam capable, through physical action as a sponge, of taking up wound exudate. The polyurethane mass may contain antibacterial substances and growth factors. Superabsorbents useful as a moisture-binding constituent are not mentioned, nor are any examples provided as to how antibacterial substances or growth factors can be incorporated in the polyurethane.
EP 1 175 148 A1 claims polymeric wound contact materials composed of PU foams in whose structure the antiseptic, including PHMB, is chemically bound to the polymeric structure through covalent bonding. Here, the covalent bonding to the supporting PU foam means that bioavailability is only limited.
EP 0 106 439 A1 and GB 2 290 031 A1 describe multilayered polymeric wound contact materials comprising a polyurethane foam interlayer in which the therapeutically acting substances can be incorporated by impregnation, for example, although there is no detailed description as to the form in which the therapeutically acting substances are present and to what extent they are available to the wound to be treated.
GB 2 170 713 A1 describes explicitly microporous PU foams useful as wound contact materials which are impregnated through the action of absorbing an antiseptic solution; here, the therapeutic is only temporarily available until it is flushed out by wound exudate for example.
WO 02/100450 A1 describes medicated polyurethane gels, optionally in the form of a foam, for use on skin and/or wounds, the gels containing an active ingredient for transdermal application which is present in homogeneous form.
DD 139942 describes a process for producing single-layered PU foam wound contact materials having an antibacterial or some other therapeutic effect; however, the process always appears to require the addition of a hydrophilic substance other than the active component, for example carbohydrates in proportions of 1-50% or some other granulation-promoting hydrophilic agent.
PHMB has been widely described in the literature as an antiseptic agent.
WO 99/40791 A1 describes for example a water-insoluble, transparent, adherent, antimicrobial film which is applied to surfaces and has both a short-term and a long-term disinfecting effect. The antimicrobial film comprises an organic biguanide polymer and also antimicrobial metallic material.
U.S. Pat. No. 5,869,073 A1 describes a liquid composition for surface coating. The liquid composition consists of a solution, dispersion or suspension of a biguanidic polymer and antimicrobial metallic material.
The additional use of the biocidal metallic material makes the fabrication of the wound contact materials obtained therefrom inconvenient and costly.
US 2004/0028722 A1 and WO 02/03899 A1 describe a cellulose wound dressing for chronic wounds which contains antimicrobial additives, for example PHMB. Cellulose as a carrier material has the disadvantage of tending to stick to the wound, and this makes changing the dressing inconvenient and may impair the healing process.
WO 97/05910 A1 describes cellulose material containing a mixture of PHMB and of an anionic polymer such as polyacrylic acid superabsorbent for example. The material described is used in diapers and sanitary napkins, there is no mention of a use in the sector of wound management.
U.S. Pat. No. 4,643,181 A describes a surgical dressing comprising a substrate coated with an antimicrobial adhesive layer. The antimicrobial agent is PHMB in certain particle sizes. The presence of PHMB in the adhesive layer, however, cannot preclude the possibility of the rest of the dressing material being colonized by bacteria.
Similarly, WO 88/01877 A1 describes a hydrophilic PU wound dressing comprising a hydrophilic gel-adhesive layer which may contain active antimicrobial ingredients as well as other ingredients. Hydrogelic adhesive layers generally have but a very limited capacity for taking up wound exudate. Since, frequently, a polymeric foam layer has to be additionally included for this purpose, fabrication of the wound dressing becomes inconvenient and costly.